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U.K. set for 4-day party to mark Queen Elizabeth II's Diamond Jubilee

(CBS News) LONDON - Britain's massive celebration of Queen Elizabeth II's Diamond Jubilee Diamond is about to get into full swing.

Starting Saturday, the four-day holiday weekend will feature plenty of pomp and pageantry.

The eyes of the world were last on London for the wedding of Prince William and his beloved bride, Kate Middleton, who became known as Catherine, Duchess of Cambridge.

But celebrations surrounding their big day will seem almost modest compared to those for Queen Elizabeth II who, on this, her Diamond Jubilee, marks 60 years on the throne.

The longevity of her reign is, "a good innings, isn't it? It's really remarkable," observes Sir Peter Westmacott, Britain's Ambassador to the U.S. "The monarchy, and the Queen herself, is as popular, if not more popular than ever."

Over six decades of service, the Queen has made 325 overseas visits, been patron to more than 600 charities, and given audience to 12 prime ministers.

"She sees the prime minister every Tuesday," Brown says. ... (Former Prime Minister) Tony Blair said how comforting he found it that, whatever crisis he was in at the time, the Queen had always seen something similar (at) some other time."

To mark their matriarch's diamond year, the royal family has been touring at home and abroad.

While the Queen smiled and waved her way through the United Kingdom with the help of Catherine, Prince Harry took his first solo tour, to Belize, the Bahamas, and Jamaica.

"Her Majesty has asked me to extend her great good wishes to you all and is sorry she can't be here, so you're stuck with me!" Harry joked in a speech.

And in Brazil, he told CBS News it was an honor. "To me, she's just 'Granny,"' Harry said. "But to all these countries, she's the queen and she's, you know, this, this great thing that they respect and love."

Over the next four days, millions are expected to line London's streets for festivities.

On Sunday, Jubilee bells will ring out as a 1,000-boat flotilla carries the royal family down the River Thames, through the heart of London. It will be the largest flotilla on the Thames since World War II.

The stage is being set for an all-star concert at Buckingham Palace where, on Friday morning, troops took part in a full-pageant dress rehearsal.

It's a party undeniably fit for a queen, as the nation and world celebrate and reflect.

It's important to have the mass celebration of the milestone, says Westmacott, because "people want to say 'thank you, well done, fantastic achievement to have done this 60 years and still to be on top of your game, and long may she reign over lus."'

There are countless events planned throughout the U.K. over the next four days.

Many in London are looking forward to Sunday's street parties. Officials estimate twice as many people will turn out as did for last year's royal wedding.

On Tuesday, the final day of the Diamond Jubilee weekend, the Queen and the royal family will attend a national service of Thanksgiving at London's St. Paul's Cathedral.